The present invention relates generally to conduit construction equipment and methods, and particularly to pipe section placement equipment and a method of multiple pipe section manipulation and placement.
A traditional method of underground conduit construction is by casting length sections of conduit in place within a tunnel formation. An underground tunnel is first excavated along a line of intended conduit placement and a steel form is assembled within the tunnel to provide an inner cavity defining the conduit passageway. The annular region surrounding the steel form and extending to the tunnel wall is filled with high strength structural concrete. The structural concrete is placed around the steel form using concrete pumps and slickline drawn along the top of the form to fill the length of the annular region surrounding the forms. As the concrete cures, some voids at the tunnel arch may exist and must be filled using preplaced plumbing mounted along the tunnel arch. This cast-in-place method is limited to approximately 150 feet of conduit construction per day. Time is required for placement of the steel forms, for the concrete to cure and to fill the arch voids. Also, this cast in place method of conduit construction requires large volumes of expensive high strength structural quality concrete.
A more recent method of underground conduit construction is by end-to-end abutment and precise alignment of preformed steel reinforced concrete pipe sections within a tunnel formation. By using preformed pipe sections, the annular region of the tunnel exterior of the pipe section may be filled with less expensive concrete, i.e. lower strength cement, without degradation in overall conduit quality. Less material costs are incurred with respect to filling in the annular cavity, i.e., the tunnel volume exterior of the conduit because less high strength structural concrete is needed. Use of preformed pipe sections, however, introduces additional complexity with respect to delivery and manipulation of pipe sections within the tunnel formation.
A typical installation uses mating bell and spigot formations on abutting pipe section ends to accomplish section joining. In addition to precise longitudinal bell and spigot engagement and alignment of the pipe sections relative to line and grade requirements, pipe sections typically must be rotatably aligned. For example, each pipe section may have a portion of its inner surface treated or lined to be used as protection against gas related corrosion. Thus, pipe section placement often requires rotation about the longitudinal axis of each pipe section to align such portions prior to end-to-end abutment. For large conduit projects, individual pipe sections may be anywhere from 10 to 15 feet in diameter and 12 to 24 feet in length. The weight of these large pipe sections is enormous.
Typically a rail system is constructed along the length of the tunnel floor to transport muck from the digging operation. Once the tunnel is constructed, the pipe sections are brought into the tunnel using the same rail system. The rail system rails are typically along the centerline of the tunnel formation, but as a practical matter the intended line and grade of conduit placement varies from the tunnel center line. Accordingly, as the pipe sections are delivered by way of the rail system to the placement site, lateral shifting of the pipe sections is often required to bring the pipe sections in line with the intended line of conduit placement.
Once pipe placement begins at a given point in the tunnel, the pipe sections are delivered to the conduit only by way of the "open" portion of the tunnel, i.e. the portion without pipe sections in place. The rail system, therefore, is a limited resource with respect to pipe section transport. More particularly, because only a single rail system may be provided within a tunnel formation, only one locomotive transporting a single pipe section has been used on the rail system at any given time, either traveling to the placement site or returning from the placement site. The rail system is typically dismantled and removed from the tunnel as the conduit is constructed, but also sometimes left in place. Accordingly, the placement site can become cluttered and unworkable if not maintained by removal of items such as rail carts used to deliver pipe sections, portions of the dismantled rail system and other construction debris not forming a portion of the conduit. There is little room to manipulate the pipe sections even without such articles cluttering the placement site. Generally pipe section transport has represented a significant time consuming aspect of pipe placement.
Given the substantial size and weight of the pipe section, the need for precise, and in many cases extensive, manipulation prior to placement, and the need to maintain the placement site free of clutter, conduit construction by the method of preformed pipe sections has been slow. Each pipe section is individually transferred to the placement site, sometimes moved laterally from the rail system to alignment with the intended line of conduit placement, aligned rotationally with the conduit, abutted at its proximal end into the conduit, positioned at its distal end according to specified line and grade, and blocked at line and grade prior to filling the tunnel void exterior of the pipe sections. Such extensive manipulation of massive pipe sections and maintenance of the placement site within the close confines of the tunnel formation makes pipe section placement a complex task.
Prior methods of pipe section placement have been limited to single pipe section manipulation at a given time. Because of the need for extensive manipulation to accomplish pipe section placement and the limited transportation resources within the open portion of the tunnel, only one pipe section at a time is delivered to the pipe placement crew. While the pipe placement crew manipulates the pipe section for placement, the pipe transport crew returns to the tunnel opening to get the next pipe section. A significant time consuming activity has been pipe transport, and this has influenced the total amount of conduit construction possible in a given time period.
According to one prior method of conduit construction, a pipe transport machine moves a single pipe section down the tunnel on the rail system and places the pipe section at the open end of the conduit. A pipe placement machine positioned within the conduit performs the task of pipe section placement. Each pipe section must be individually placed immediately adjacent the conduit opening in order to allow the placement machine to lift and manipulate the pipe section into place. In this method of pipe placement, essentially only one unplaced pipe section resides within the tunnel at a given time. The tasks of pipe transport and pipe placement are sequential per individual pipe section and therefore limited to manipulation of but one pipe section.
According to prior methods of pipe section placement there always existed significant interdependence between the task of pipe transport to a suitable delivery point at the placement site and the task of pipe placement from the delivery point. This interdependence has limited the total number of pipe sections which could be placed in a given time period, and therefore contributed substantially to overall project costs.